Can we Validate Twin Studies? A Census-Based Heritability Estimate of Educational Achievement

Abstract

For most phenotypes, the amount of variance explained by SNPs is generally lower than the amount of additive genetic variance estimated in twin studies. This is also true for educational achievement. Twin-based estimates may... [ view full abstract ]

For most phenotypes, the amount of variance explained by SNPs is generally lower than the amount of additive genetic variance estimated in twin studies. This is also true for educational achievement. Twin-based estimates may be biased because of self-selection and differences in cognitive ability between twins and the rest of the population. Here we compare twin registry based estimates with a census-based heritability estimate, sampling from the same birth cohort population and the same standardized measure for educational achievement. We analyzed 893,127 scores on a Dutch test administered at the end of primary school, from the years 2008-2014. For genetic inference, we used pedigree information to construct an additive genetic relationship matrix. We analyzed the data using a Bayesian linear mixed model, including important covariates. Corrected for these covariates, this resulted in an estimate of 83%, which is even higher than based on twin studies using the same cohort and measure. We therefore conclude that the genetic variance not tagged by SNPs is not an artefact of the twin method itself.